Protective effects of a novel 32-amino acid C-terminal fragment of CAP18 in endotoxemic pigs

A Hybrid Peptide DEFB-TP5 Expressed in Methylotrophic Yeast Neutralizes LPS With Potent Anti-inflammatory Activities

DEFB-TP5 is a novel auspicious health-beneficial peptide derivative from two naturally occurring peptides, β-Defensin (DEFB) and thymopentin (TP5), and shows strong anti-inflammatory activity and binds to LPS without cytotoxicity and hemolytic effect. Furthermore, the application of DEFB-TP5 peptide is inadequate by its high cost. In the current study, we developed a biocompatible mechanism for expression of the DEFB-TP5 peptide in Pichia pastoris. The transgenic strain of hybrid DEFB-TP5 peptide with a molecular weight of 6.7kDa as predictable was obtained. The recombinant DEFB-TP5 peptide was purified by Ni-NTA chromatography, estimated 30.41 mg/L was obtained from the cell culture medium with 98.2% purity. Additionally, The purified DEFB-TP5 peptide significantly (p< 0.05) diminished the release of nitric oxide (NO), TNF-α, IL-6, IL-1β in LPS-stimulated RAW264.7 macrophages in a dose-dependent manner. This study will not only help to understand the molecular mechanism of expression that can potentially be used to develop an anti-endotoxin peptide but also to serve as the basis for the development of antimicrobial and anti-inflammatory agents as well, which also provides a potential source for the production of recombinant bioactive DEFB-TP5 at the industrial level.

Delayed therapy with a polymyxin B-dextran conjugate (PMX-622) improves survival in rabbits with Gram-negative peritonitis

Polymyxin B (PMB) is an amphipathic nephrotoxic antibiotic, which has been shown to neutralize the effects of endotoxin both in vitro and in vivo. PMB-D70 (PMX-622), a covalent conjugate of PMB with dextran 70 (D70), is less nephrotoxic than the parent compound. We sought to determine whether therapy with PMB-D70, in addition to conventional antimicrobial chemotherapy, could improve survival in a model of Gram-negative peritonitis. At T = 0 h, New Zealand white rabbits were implanted intraperitoneally with 10 ml of a suspension containing hemoglobin (40 μg/ml), mucin (150 μg/ml), and 1.0 ± 0.2 x 104 cfu/kg of viable Escherichia coli (O18:K1). Beginning at T = 4 h, the rabbits were treated with gentamicin (5 mg/kg every 12 h) for five doses or until death, and infused for 24 h or until death with either D70 or PMB-D70. Two pairs of groups were studied (doses indicate cumulative amounts infused over 24 h). The PMB-D70 (low dose) group received PMB-D70 (5 mg/kg of the PMB component) and the D70 (low dose) group received an equivalent dose of D70. The PMB-D70 (high dose) group received PMB-D70 (10 mg/kg of the PMB component) and the D70 (high dose) group received an equivalent dose of D70. Results for the two PMB-D70 groups, on the one hand, and the two D70 group, on the other hand, were statistically indistiguishable and, accordingly, were pooled for all analyses. Survival at 7 days was 11/25 (44%) for rabbits treated with PMB-D70 as compared to 2/23 (9%) for animals treated with D70 ( P = 0.007). We conclude that adjuvant treatment with PMB-D70 improves survival in a clinically relevant model of Gram-negative sepsis.

TALF peptide-immunoglobulin G conjugates that bind lipopolysaccharide

Several peptides mimicking the amino acid sequence of Tachypleus anti-LPS factor (TALF) bind LPS with high affinity and some neutralize LPS in vitro and in vivo (Kloczewiak M., Black K.M., Loiselle P., Cavaillon J-M., Wainwright N., Warren H.S. Synthetic peptides that mimic the binding site of horseshoe crab anti-lipopolysaccharide factor. J Infect Dis 1994; 170: 1490-1497). Two such peptides, TALF29-59 and TALF41-53, were covalently coupled to human IgG via a disulfide bond using the heterobifunctional linker, N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP). The resulting peptide-lgG conjugates contained 4-8 moles peptide per mole IgG and were evaluated for the ability to bind and neutralize LPS. Both conjugates bound LPS in a LPS capture Western blot assay. In a fluid-phase radioimmunoassay, half-maximal binding of 5 μg/ml LPS by many different Escherichia coli strains occurred at 50-100 μg/ml for both conjugates. Coagulation of Limulus amoebocyte lysate was only minimally inhibited by 5 μg/ml of each conjugate. Our data suggest that TALF peptide-lgG conjugates bind LPS with high affinity, but only weakly neutralize LPS. These studies provide an initial step towards the development of peptide-lgG preparations that might be useful for the treatment of Gram-negative sepsis by binding and clearing LPS.

Anti-endotoxin properties of cationic host defence peptides and proteins

The innate immune system of mammals contains a series of peptides with overall positive charge and an amphipathic structure which have a variety of important properties in host defences. Although these are often termed cationic antimicrobial peptides, they have numerous roles in innate defences in all complex species of life and thus we prefer to refer to them as host defence peptides. These roles include: (i) an ability to kill micro-organisms directly, ranging from bacteria to viruses, fungi, parasites and helminths; (ii) an adjuvant activity in the adaptive response; and (iii) a multiplicity of roles in modulating innate immunity, including an apparent ability to stimulate protective innate immunity while suppressing harmful inflammatory/septic responses. This latter property may be one of the more important activities of these peptides in vivo. Innate immunity is thought to be triggered by the interaction of conserved bacterial components with particular receptors including Toll-like receptors (TLRs) on host cells. However, the initiation of the innate immune response through this route may trigger a pro-inflammatory cascade that is the principle cause of harmful conditions such as sepsis. Since we are exposed to potentially dangerous pathogens on a daily basis, the host response must contain certain checks and balances. We propose that host defence peptides have a role in feed-back modulation of inflammation under normal (low-pathogen exposure) conditions. This review surveys the available information regarding the antiendotoxic/anti-inflammatory properties of host defence peptides, and will address whether this potential might be exploited for therapeutic benefit in sepsis.

Rational design of engineered cationic antimicrobial peptides consisting exclusively of arginine and tryptophan, and their activity against multidrug-resistant pathogens

The emergence of multidrug-resistant (MDR) pathogens underscores the need for new antimicrobial agents to overcome the resistance mechanisms of these organisms. Cationic antimicrobial peptides (CAPs) provide a potential source of new antimicrobial therapeutics. We previously characterized a lytic base unit (LBU) series of engineered CAPs (eCAPs) of 12 to 48 residues demonstrating maximum antibacterial selectivity at 24 residues. Further, Trp substitution in LBU sequences increased activity against both P. aeruginosa and S. aureus under challenging conditions (e.g., saline, divalent cations, and serum). Based on these findings, we hypothesized that the optimal length and, therefore, the cost for maximum eCAP activity under physiologically relevant conditions could be significantly reduced using only Arg and Trp arranged to form idealized amphipathic helices. Hence, we developed a novel peptide series, composed only of Arg and Trp, in a sequence predicted and verified by circular dichroism to fold into optimized amphipathic helices. The most effective antimicrobial activity was achieved at 12 residues in length (WR12) against a panel of both Gram-negative and Gram-positive clinical isolates, including extensively drug-resistant strains, in saline and broth culture and at various pH values. The results demonstrate that the rational design of CAPs can lead to a significant reduction in the length and the number of amino acids used in peptide design to achieve optimal potency and selectivity against specific pathogens.

[Progress in cathelicidins antimicrobial peptides research]

Cathelicidins are a family of multi-functional antimicrobial peptides found in almost all types of vertebrates, where they play vital roles in the immune system. As they possess broad-spectrum antimicrobial properties, cathelicidins are not only strongly resistant to Gram-positive and Gram-negative bacteria, fungi, and viruses, but they are also active against many antibiotic-resistant clinical bacteria, adopting a special antimicrobial mechanism that is unlikely to lead to microbial resistance. Cathelicidins likewise possess simple structures, and low hemolytic and cytotoxic activities. Collectively, these features suggest potentially novel and exciting prospects for cathelicidins' application in medicine. Here, we review the structures, classification, activities, mechanisms, as well as prospective developments in the usage and application of cathelicidin antimicrobial peptides.

Determination of the antibacterial and lipopolysaccharide-neutralizing regions of guinea pig neutrophil cathelicidin peptide CAP11

Previously, we revealed that a cationic antibacterial polypeptide of 11 kDa (CAP11), a member of the cathelicidins isolated from guinea pig neutrophils, exhibits not only potent antibacterial activity but also lipopolysaccharide (LPS)-neutralizing activity. In this study, to determine the biologically active regions of CAP11, we isolated or synthesized the partial peptides of CAP11 and evaluated their antibacterial and LPS-neutralizing activities. Although CAP11 has a unique homodimeric structure with a disulfide bridge, the biological activities of dimeric and monomeric forms of CAP11 were almost the same. Moreover, the G(1)-E(33) peptide of CAP11 showed the same activities as CAP11, whereas the C-terminal region (Y(34) to I(43)) possessed no biological activities. In addition, the three 18-mer peptides (G(1)-R(18), T(9)-K(26), and L(16)-E(33)) with overlapping sequences were synthesized, and their activities were determined. The three 18-mer peptides retained the antibacterial activities, and G(1)-R(18) was the most potent. In contrast, the LPS-neutralizing activities of these peptides were markedly reduced. Together, these observations indicate that the active region with antibacterial activity is localized at G(1) to R(18) of CAP11, whereas longer sequences (such as G(1) to E(33)) would be required for the expression of LPS-neutralizing activity. Furthermore, the C-terminal region (Y(34) to I(43)) and a disulfide bridge are not essential for the antibacterial and LPS-neutralizing activities of CAP11.

Immunomodulatory properties of defensins and cathelicidins

Host defence peptides are a conserved component of the innate immune response in all complex life forms. In humans, the major classes of host defence peptides include the α- and β-defensins and the cathelicidin, hCAP-18/LL-37. These peptides are expressed in the granules of neutrophils and by a wide variety of tissue types. They have many roles in the immune response including both indirect and direct antimicrobial activity, the ability to act as chemokines as well as induce chemokine production leading to recruitment of leukocytes to the site of infection, the promotion of wound healing and an ability to modulate adaptive immunity. It appears that many of these properties are mediated though direct interaction of peptides with the cells of the innate immune response including monocytes, dendritic cells, T cells and epithelial cells. The importance of these peptides in immune responses has been demonstrated since animals defective in the expression of certain host defence peptides showgreater susceptibility to bacterial infections. In the very few instances in which human patients have been demonstrated to have defective host defence peptide expression, these individuals suffer from frequent infections. Although studies of the immunomodulatory properties of these peptides are in their infancy, there is a growing body of evidence suggesting that the immunomodulatory properties of these small, naturally occurring molecules might be harnessed for development as novel therapeutic agents.

Human cathelicidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3

The innate immune system of mammals provides a rapid response to repel assaults from numerous infectious agents including bacteria, viruses, fungi, and parasites. A major component of this system is a diverse combination of cationic antimicrobial peptides that include the alpha- and beta-defensins and cathelicidins. In this study, we show that 1,25-dihydroxyvitamin D3 and three of its analogs induced expression of the human cathelicidin antimicrobial peptide (CAMP) gene. This induction was observed in acute myeloid leukemia (AML), immortalized keratinocyte, and colon cancer cell lines, as well as normal human bone marrow (BM) -derived macrophages and fresh BM cells from two normal individuals and one AML patient. The induction occurred via a consensus vitamin D response element (VDRE) in the CAMP promoter that was bound by the vitamin D receptor (VDR). Induction of CAMP in murine cells was not observed and expression of CAMP mRNA in murine VDR-deficient bone marrow was similar to wild-type levels. Comparison of mammalian genomes revealed evolutionary conservation of the VDRE in a short interspersed nuclear element or SINE in the CAMP promoter of primates that was absent in the mouse, rat, and canine genomes. Our findings reveal a novel activity of 1,25-dihydroxyvitamin D3 and the VDR in regulation of primate innate immunity.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Novel therapies for sepsis: antiendotoxin therapies

Severe sepsis and septic shock is a common problem encountered in the critical care unit with an estimated incidence in the US of 750,000 cases/year and a mortality rate of 30-50%. Sepsis involves a complex interaction between bacterial factors and the host immune system producing a systemic inflammatory state that may progress to multiple organ failure and death. Endotoxin (a lipopolysaccharide) released from Gram-negative bacteria has been implicated as a potent, prototypical stimulus of the immune response to bacterial infection. Current antiendotoxin strategies utilise various approaches ranging from the prevention of binding to endotoxin receptors with antibodies (monoclonal or polyclonal) against endotoxin or endotoxin receptor/carrier molecules (antiCD14 or antilipopolysaccharide-binding protein antibodies), enhancing clearance or neutralisation (haemoperfusion, lipoproteins, lipopolysaccharide-neutralising proteins) or impairing cellular signalling (lipid A analogues, tyrosine kinase inhibitors). In the future, innovative therapies involving Toll-like receptors and their downstream signalling elements will be developed. This review discusses current knowledge regarding endotoxin signalling, antiendotoxin therapies currently under development, and future areas for research.

Augmentation of the lipopolysaccharide-neutralizing activities of human cathelicidin CAP18/LL-37-derived antimicrobial peptides by replacement with hydrophobic and cationic amino acid residues

Mammalian myeloid and epithelial cells express various peptide antibiotics (such as defensins and cathelicidins) that contribute to the innate host defense against invading microorganisms. Among these peptides, human cathelicidin CAP18/LL-37 (L(1) to S(37)) possesses not only potent antibacterial activity against gram-positive and gram-negative bacteria but also the ability to bind to gram-negative lipopolysaccharide (LPS) and neutralize its biological activities. In this study, to develop peptide derivatives with improved LPS-neutralizing activities, we utilized an 18-mer peptide (K(15) to V(32)) of LL-37 as a template and evaluated the activities of modified peptides by using the CD14(+) murine macrophage cell line RAW 264.7 and the murine endotoxin shock model. By replacement of E(16) and K(25) with two L residues, the hydrophobicity of the peptide (18-mer LL) was increased, and by further replacement of Q(22), D(26), and N(30) with three K residues, the cationicity of the peptide (18-mer LLKKK) was enhanced. Among peptide derivatives, 18-mer LLKKK displayed the most powerful LPS-neutralizing activity: it was most potent at binding to LPS, inhibiting the interaction between LPS and LPS-binding protein, and attaching to the CD14 molecule, thereby suppressing the binding of LPS to CD14(+) cells and attenuating production of tumor necrosis factor alpha (TNF-alpha) by these cells. Furthermore, in the murine endotoxin shock model, 18-mer LLKKK most effectively suppressed LPS-induced TNF-alpha production and protected mice from lethal endotoxin shock. Together, these observations indicate that the LPS-neutralizing activities of the amphipathic human CAP18/LL-37-derived 18-mer peptide can be augmented by modifying its hydrophobicity and cationicity, and that 18-mer LLKKK is the most potent of the peptide derivatives, with therapeutic potential for gram-negative bacterial endotoxin shock.

Cathelicidins: microbicidal activity, mechanisms of action, and roles in innate immunity

Antimicrobial peptides are important host-defense molecules of innate immunity. Cathelicidins are a diverse family of potent, rapidly acting and broadly effective antimicrobial peptides, which are produced by a variety of cells. This review examines the classification, antimicrobial spectrum, mechanism of action, and regulation of cathelicidins.

Structural features and biological activities of the cathelicidin-derived antimicrobial peptides

Cathelicidins are a numerous group of mammalian proteins that carry diverse antimicrobial peptides at the C-terminus of a highly conserved preproregion. These peptides, which become active when released from the proregion, display a remarkable variety of sizes, sequences, and structures, and in fact comprise representatives of all the structural groups in which the known antimicrobial peptides have been classified. Most of the cathelicidin-derived peptides exert a broad spectrum and potent antimicrobial activity and also bind to lipopolysaccharide and neutralize its effects. In addition, some of them have recently been shown to exert other activities and might participate in host defense also by virtue of their ability to induce expression of molecules involved in a variety of biological processes. This review is aimed at providing a general overview of the cathelicidins and of the peptides derived therefrom, with emphasis on aspects such as structure, biological activities in vitro and in vivo, and structure/activity relationship studies.

Cutting edge: cationic antimicrobial peptides block the binding of lipopolysaccharide (LPS) to LPS binding protein

We investigated the mechanism by which cationic antimicrobial peptides block the activation of macrophages by LPS. The initial step in LPS signaling is the transfer of LPS to CD14 by LPS binding protein (LBP). Because many cationic antimicrobial peptides bind LPS, we asked whether these peptides block the binding of LPS to LBP. Using an assay that measures the binding of LPS to immobilized LBP, we show for the first time that a variety of structurally diverse cationic antimicrobial peptides block the interaction of LPS with LBP. The relative ability of different cationic peptides to block the binding of LPS to LBP correlated with their ability to block LPS-induced TNF-alpha production by the RAW 264.7 macrophage cell line.

Antiendotoxin strategies

Endotoxin is a potent stimulator of the inflammatory response and is believed to initiate the pathology in Gram-negative sepsis. Agents are being developed that bind and neutralize or block the effects of endotoxin, with the goal of improving outcome in the treatment of sepsis. Strategies discussed in this article include anti-LPS antibodies, LPS binding proteins and lipoproteins, polymyxin B conjugates, lipid A analogues, and extracorporeal techniques for endotoxin removal.

The human cationic antimicrobial protein (hCAP18), a peptide antibiotic, is widely expressed in human squamous epithelia and colocalizes with interleukin-6

Peptide antibiotics are widespread in nature and, by providing a rapid first line of defense, may be key players in the innate immune system. Although epithelia are the main barriers shielding the internal environment from microorganisms, the role for peptide antibiotics in epithelial protection is unclear. We recently reported that the human cationic antimicrobial protein hCAP18, the precursor of the antimicrobial peptide called LL-37, is not expressed by normal human keratinocytes but is induced in various inflammatory skin disorders. In the present study we demonstrate that hCAP18 is consistently expressed at both mRNA and protein levels in squamous epithelia of the mouth, tongue, esophagus, cervix, and vagina in humans. The gene for hCAP18 contains promoter elements that are potentially regulated by interleukin-6, and our data further show a colocalization between interleukin-6 and hCAP18 expression in these tissues. Our finding that hCAP18 is widely produced in squamous epithelia suggests a role for this peptide in epithelial antimicrobial defense. Furthermore, colocalization with interleukin-6 indicates a potential local mechanism for the upregulation of hCAP18 at the epithelial surfaces.

Evaluation of antimicrobial and lipopolysaccharide-neutralizing effects of a synthetic CAP18 fragment against Pseudomonas aeruginosa in a mouse model

CAP18 (cationic antimicrobial protein; 18 kDa) is a neutrophil-derived protein that can bind to and inhibit various activities of lipopolysaccharide (LPS). The 37 C-terminal amino acids of CAP18 make up the LPS-binding domain. A truncated 32-amino-acid C-terminal fragment of CAP18 had potent activity against Pseudomonas aeruginosa in vitro. We studied the antimicrobial and LPS-neutralizing effects of this synthetic truncated CAP18 peptide (CAP18106-137) on lung injury in mice infected with cytotoxic P. aeruginosa. To determine its maximal effect, the CAP18106-137 peptide was mixed with bacteria just prior to tracheal instillation, and lung injury was evaluated by determining the amount of leakage of an alveolar protein tracer (125I-albumin) into the circulation and by the quantification of lung edema. The lung injury caused by the instillation of 5 x 10(5) CFU of P. aeruginosa was significantly reduced by the concomitant instillation of CAP18106-137. However, the administration of CAP18106-137 alone, without bacteria, induced lung edema, suggesting that it has some toxicity. Also, the peptide did not significantly reduce the number of bacteria that had been simultaneously instilled, nor did it significantly improve the survival of the infected mice. The addition of CAP18106-137 to aztreonam along with the bacteria did decrease the level of antibiotic-induced release of inflammatory mediators including tumor necrosis factor alpha, interleukin-6, and nitric oxide and also improved the survival of the mice. Therefore, more investigations are needed to confirm the toxicities and the therapeutic benefits of CAP18106-137 as an adjunctive therapy to antibiotics in the treatment of infections caused by gram-negative bacteria.

Activities of LL-37, a cathelin-associated antimicrobial peptide of human neutrophils

Human neutrophils contain two structurally distinct types of antimicrobial peptides, beta-sheet defensins (HNP-1 to HNP-4) and the alpha-helical peptide LL-37. We used radial diffusion assays and an improved National Committee for Clinical Laboratory Standards-type broth microdilution assay to compare the antimicrobial properties of LL-37, HNP-1, and protegrin (PG-1). Although generally less potent than PG-1, LL-37 showed considerable activity (MIC, <10 microgram/ml) against Pseudomonas aeruginosa, Salmonella typhimurium, Escherichia coli, Listeria monocytogenes, Staphylococcus epidermidis, Staphylococcus aureus, and vancomycin-resistant enterococci, even in media that contained 100 mM NaCl. Certain organisms (methicillin-resistant S. aureus, Proteus mirabilis, and Candida albicans) were resistant to LL-37 in media that contained 100 mM NaCl but were susceptible in low-salt media. Burkholderia cepacia was resistant to LL-37, PG-1, and HNP-1 in low- or high-salt media. LL-37 caused outer and inner membrane permeabilization of E. coli ML-35p. Chromogenic Limulus assays revealed that LL-37 bound to E. coli O111:B4 lipopolysaccharide (LPS) with a high affinity and that this binding showed positive cooperativity (Hill coefficient = 2.02). Circular dichroism spectrometry disclosed that LL-37 underwent conformational change in the presence of lipid A, transitioning from a random coil to an alpha-helical structure. The broad-spectrum antimicrobial properties of LL-37, its presence in neutrophils, and its inducibility in keratinocytes all suggest that this peptide and its precursor (hCAP-18) may protect skin and other tissues from bacterial intrusions and LPS-induced toxicity. The potent activity of LL-37 against P. aeruginosa, including mucoid and antibiotic-resistant strains, suggests that it or related molecules might have utility as topical bronchopulmonary microbicides in cystic fibrosis.

Protective effects of a human 18-kilodalton cationic antimicrobial protein (CAP18)-derived peptide against murine endotoxemia

CAP18 (an 18-kDa cationic antimicrobial protein) is a granulocyte-derived protein that can bind lipopolysaccharide (LPS) and inhibit various activities of LPS in vitro. The present study examined the protective effect of a synthetic 27-amino-acid peptide (CAP18(109-135)) from the LPS-binding domain of CAP18 against antibiotic-induced endotoxin shock, using highly LPS-sensitive D-(+)-galactosamine (D-GalN)-sensitized C3H/HeN mice. The antibiotic-induced endotoxin (CAZ-endotoxin) was prepared from the culture filtrate of Pseudomonas aeruginosa PAO1 exposed to ceftazidime (CAZ). Injection of CAP18(109-135) protected the mice injected with LPS or CAZ-endotoxin from death and lowered their tumor necrosis factor (TNF) levels in serum in a dose-dependent manner. Treatment with CAZ caused death of the D-GalN-sensitized P. aeruginosa PAO-infected mice within 48 h, while injection with CAP18(109-135) rescued the mice from death. In the mice rescued from death by injection with CAP18(109-135), endotoxin levels in plasma and TNF production by liver tissues were decreased but the numbers of viable infecting bacteria in their blood were not decreased significantly and remained at the levels in CAZ-treated mice. These results indicate that CAP18(109-135) is capable of preventing antibiotic-induced endotoxic shock in mice with septicemia and that the effect is due to its LPS-neutralizing activity rather than to its antibacterial activity.

Effect of anticoagulants on binding and neutralization of lipopolysaccharide by the peptide immunoglobulin conjugate CAP18(106-138)-immunoglobulin G in whole blood

The 18-kDa cationic protein CAP18 is an antimicrobial protein isolated from rabbit granulocytes that binds lipopolysaccharide (LPS) and inhibits many of its biological activities. We covalently coupled a synthetic peptide representing amino acids 106 to 138 of CAP18 to human immunoglobulin G (IgG) by using the heterobifunctional linker N-succinimidyl-3-(2-pyridyidithio)propionate. The ability of CAP18(106-138)-IgG to bind and neutralize LPS in whole blood in the presence and absence of anticoagulants was studied. Both CAP18(106-138) and CAP18(106-138)-IgG significantly suppressed LPS-induced tumor necrosis factor (TNF) production in whole blood in the absence of anticoagulants. EDTA potentiated the ability of CAP18(106-138) and CAP18(106-138)-IgG to decrease LPS-induced TNF production in a dose-dependent manner. In contrast, heparin inhibited the ability of CAP18(106-138) and CAP18(106-138)-IgG to suppress LPS-induced TNF production. EDTA also enhanced LPS capture in a fluid-phase binding assay that utilizes magnetic anti-IgG beads to capture CAP18(106-138)-IgG (and bound [3H]LPS) in whole blood. In contrast, heparin inhibited the binding dose dependently. We conclude that CAP18(106-138)-IgG binds to and neutralizes LPS in whole blood in the absence of anticoagulants. Further studies of its protective efficacy in animal models are warranted. Caution should be used in interpreting assays that measure the binding and neutralization of LPS in whole blood in the presence of calcium-binding anticoagulants or heparin.

Structural, functional analysis and localization of the human CAP18 gene

CAP18 is an antimicrobial protein found in specific granules of PMNs. The human CAP18 (HCAP18) gene was cloned from a human genomic phage library. Sequence analysis revealed the HCAP18 gene to have 4 exons spanning 3 kb, including 700 bp of upstream DNA. Using 3' RACE no homologs of human HCAP18 were found in human bone marrow or leukocyte populations. By PCR analysis of a somatic cell mapping panel and fluorescence in situ hybridization of a genomic clone to metaphase chromosomes the gene was mapped to chromosome band 3p21.3. Like several other genes expressed late in PMN development the CAP18 gene did not contain typical TATA box or CCAAT sequences. Expression in Cos 7 cells permitted limited mapping of the promoter function in upstream fragments of the HCAP18 gene. Western blot, Northern blot and RT-PCR analysis show HCAP18 to be produced specifically in granulocytes. This work forms the groundwork for future analysis of the genetic regulation of this antimicrobial protein during PMN differentiation.